1. Field of the Invention
The present invention relates to an extensible structure and more particularly, it relates to an improvement of the extensible structure wherein a plurality of longerons which can be resiliently deformed like a coil are connected to one another by batten members, and chords are diagonally stretched between connected points of the adjacent longerons and a batten member and connected points of these longerons and an adjacent batten member, and wherein when the longerons are deployed like a straight line, a truss structure can be formed, while when the longerons are deformed like a coil, the structure can be collapsed.
2. Description of the Related Art
A structure of this kind is used for a space station as the support mast for solar batteries, and for other space craft. It can be used on the ground as an antenna support which can be easily assembled in an emergency, and for other uses also.
This structure includes a plurality of bendable longerons, a plurality of batten members for connecting these longerons to one another, and chords stretched between adjacent longerons and between adjacent batten members. This extensible structure is disclosed in U.S. Pat. Nos. 3,486,279 (Mauch) and 4,334,391 (Hedgepeth et al). They have rod-like batten members, and adjacent longerons are connected to each other by a batten member. U.S. Pat. Nos. 4,532,742 (Miura et al) and 4,662,130 (Miura) also relate to this extensible structure. They have star-like batten members each having plural arms radially projected from the center of the batten member, and front ends of these arms are attached to the longerons.
FIGS. 1 through 3 show one of these conventional extensible structures. This structure has three longerons and resiliently twistable and deformable batten members. FIG. 1 shows the structure extended, FIG. 2 shows it on the way to its being extended, and FIG. 3 shows it collapsed. It has disk-like end plates 1 and 2. One end of these three longerons 3, respectively, is attached to end plate 1 through hinges 4, while the other end thereof is attached to end plate 2 through hinges (not shown). The ends of longerons 3 are connected to end plates 1 and 2 through hinges in such a manner that longerons 3 can be freely rotated in the circumferential direction of these end plates 1 and 2. Longerons 3 are connected to one another by a plurality of batten members 5. Batten members 5 are arranged in the axial direction of longerons 3 with a certain interval interposed between adjacent ones. Each of batten members 5 has three arms radially projected from the center thereof, and the free ends of these arms are attached to longerons 3. When the structure is extended as shown in FIG. 1, these arms are twisted and deformed, while when it is collapsed as shown in FIG. 3, they become flat. Two chords 6 are diagonally stretched, crossing each other, between four connected points of two adjacent longerons and two batten members adjacent in the axial direction of longerons 3. Each of batten members 5 is provided with through-hole 8 in the center thereof and end plate 1 is also provided with through-hole 9 in the center thereof. Cable 7 is passed through these through-holes 8 and 9 and its foremost end is attached to the center of end plate 2. A take-up drum (not shown) is arranged under end plate 1 and the cable is wound round this take-up drum.
When the take-up drum winds up cable 7 in this extensible structure, longerons are resiliently deformed like a coil as shown in FIG. 3 and the structure can be collapsed to have an extremely small volume relative to its extended state. When the take-up drum feeds cable 7, longerons 3 are extended like a straight line by their resilient force to finally cause the structure to be erected like a straight line as shown in FIG. 1. When the structure is in the extended state shown in FIG. 1, each of chords 6 is stretched by a certain pulling force to form a truss framing, thereby enhancing the strength and stiffness of this structure.
In the case of this structure, however, each one of longerons 3 must be resiliently bendable. When the strength and stiffness of this structure are to be made high, however, the number of these longerons 3 must be increased. When the number of these longerons 3 is increased, however, the interval between adjacent ones of these longerons 3 becomes small. When the interval becomes small, the shape of a rectangle formed by four connected points between two adjacent longerons and two batten members adjacent in the axial direction of the longerons is made to have two sides long in the vertical direction of the longerons and two sides short in the horizontal direction thereof. When the diagonal chords are stretched to have an angle of 45.degree. relative to the longeron or batten member, they are usually the most effective and it is therefore practically preferable that they are stretched relative to the longeron or batten member within a range of 45.degree..+-.15.degree.. When the shape of the plane over which these chords are stretched or the shape of the rectangle formed by four connected points of the two adjacent longerons and two batten members adjacent in the axial direction of the longerons is made slender, the angle formed by the chord and the longeron falls outside the above-mentioned range. As the result, the stiffness and strength of this structure are lowered, and particularly its stiffness becomes low. In order to eliminate this drawback, it is needed that the interval of two batten members adjacent in the axial direction of the longerons is made small, corresponding to the shortened interval of the two adjacent longerons, and that the shape of the rectangular plane formed by four connected points is made more and more similar to a square. When they are arranged like this, however, the number of the batten members becomes too large and the structure becomes complicated and, thus heavy. Further, when the number of the batten members is made large in the case where the arms of the batten members are twisted and deformed as described above, the pulling load of cable 7 at the time when the structure is to be collapsed to have an extremely small volume relative to its extended state must be made large, thereby making it necessary to make the strength of this cable and that of its related mechanisms high. This causes the structure to be even heavier.